


Examples of technical principles of JavaScript event delegation_javascript skills
One of the hottest technologies in today’s JavaScript technology world should be ‘event delegation’. Using event delegation techniques allows you to avoid adding event listeners to specific each node; instead, event listeners are added to their parent elements. The event listener will analyze the events that bubble up from the child elements and find out which child element the event is from. The basic concept is very simple, but there are still many people who don't understand how event delegation works. Here I'm going to explain how event delegation works and provide a few examples of basic event delegation in pure JavaScript.
Suppose we have a UL element with several child elements:
- Item 1
- Item 2
- Item 3
- Item 4
- Item 5
- Item 6
We also assume that when each child element is clicked, a different event will occur. You can add event listeners to each independent li element, but sometimes these li elements may be deleted or added, and listening to their new or deleted events will be a nightmare, especially when your When the code that listens to the event is placed in another place in the application. But what if you place listeners on their parent elements? How do you know which child element was clicked?
Simple: When the child element's event bubbles up to the parent ul element, you can check the target attribute of the event object and capture the reference of the node element that was actually clicked. The following is a very simple JavaScript code that demonstrates the process of event delegation:
// Find the parent element and add a listener...
document.getElementById("parent-list").addEventListener("click",function(e) {
// e .target is the clicked element!
// If the li element is clicked
if(e.target && e.target.nodeName == "LI") {
// Find the target and output ID!
console.log("List item ",e.target.id.replace("post-")," was clicked!");
}
});
The first step is to add an event listener to the parent element. When an event triggers the listener, check the source of the event and exclude non-li child element events. If it is a li element, we have found the target! If it is not a li element, the event will be ignored. This example is very simple, UL and li are standard parent-child combinations. Let's experiment with some different combinations of elements. Suppose we have a parent element div with many child elements inside, but what we care about is the A tag inside with the "classA" CSS class:
// Get the parent element DIV, add a listener...
document.getElementById("myDiv").addEventListener ("click",function(e) {
// e.target is the clicked element
if(e.target && e.target.nodeName == "A") {
// Get CSS class name
var classes = e.target.className.split(" ");
// Search for matches!
if(classes) {
// For every CSS class the element has. ..
for(var x = 0; x // If it has the CSS class we want...
if(classes[x] == " classA") {
// Bingo!
console.log("Anchor element clicked!");
// Now do something here....
}
}
}
}
});
In the above example, not only the tag names are compared, but also the CSS class names are compared. Although it is a little more complicated, it is still very representative. For example, if there is a span tag in an A tag, this span will become the target element. At this time, we need to trace up the DOM tree structure to find out whether there is an A.classA element in it.
Because most programmers use jQuery and other tool libraries to handle DOM elements and events, I recommend that everyone use the event delegation method inside, because the tool library here provides advanced delegation methods and element screening. method.
I hope this article can help you understand the behind-the-scenes principles of JavaScript event delegation, and I hope you also feel the powerful use of event delegation!

I built a functional multi-tenant SaaS application (an EdTech app) with your everyday tech tool and you can do the same. First, what’s a multi-tenant SaaS application? Multi-tenant SaaS applications let you serve multiple customers from a sing

This article demonstrates frontend integration with a backend secured by Permit, building a functional EdTech SaaS application using Next.js. The frontend fetches user permissions to control UI visibility and ensures API requests adhere to role-base

JavaScript is the core language of modern web development and is widely used for its diversity and flexibility. 1) Front-end development: build dynamic web pages and single-page applications through DOM operations and modern frameworks (such as React, Vue.js, Angular). 2) Server-side development: Node.js uses a non-blocking I/O model to handle high concurrency and real-time applications. 3) Mobile and desktop application development: cross-platform development is realized through ReactNative and Electron to improve development efficiency.

The latest trends in JavaScript include the rise of TypeScript, the popularity of modern frameworks and libraries, and the application of WebAssembly. Future prospects cover more powerful type systems, the development of server-side JavaScript, the expansion of artificial intelligence and machine learning, and the potential of IoT and edge computing.

JavaScript is the cornerstone of modern web development, and its main functions include event-driven programming, dynamic content generation and asynchronous programming. 1) Event-driven programming allows web pages to change dynamically according to user operations. 2) Dynamic content generation allows page content to be adjusted according to conditions. 3) Asynchronous programming ensures that the user interface is not blocked. JavaScript is widely used in web interaction, single-page application and server-side development, greatly improving the flexibility of user experience and cross-platform development.

Python is more suitable for data science and machine learning, while JavaScript is more suitable for front-end and full-stack development. 1. Python is known for its concise syntax and rich library ecosystem, and is suitable for data analysis and web development. 2. JavaScript is the core of front-end development. Node.js supports server-side programming and is suitable for full-stack development.

JavaScript does not require installation because it is already built into modern browsers. You just need a text editor and a browser to get started. 1) In the browser environment, run it by embedding the HTML file through tags. 2) In the Node.js environment, after downloading and installing Node.js, run the JavaScript file through the command line.

How to send task notifications in Quartz In advance When using the Quartz timer to schedule a task, the execution time of the task is set by the cron expression. Now...


Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

AI Hentai Generator
Generate AI Hentai for free.

Hot Article

Hot Tools

SublimeText3 Linux new version
SublimeText3 Linux latest version

Zend Studio 13.0.1
Powerful PHP integrated development environment

SublimeText3 Chinese version
Chinese version, very easy to use

VSCode Windows 64-bit Download
A free and powerful IDE editor launched by Microsoft

mPDF
mPDF is a PHP library that can generate PDF files from UTF-8 encoded HTML. The original author, Ian Back, wrote mPDF to output PDF files "on the fly" from his website and handle different languages. It is slower than original scripts like HTML2FPDF and produces larger files when using Unicode fonts, but supports CSS styles etc. and has a lot of enhancements. Supports almost all languages, including RTL (Arabic and Hebrew) and CJK (Chinese, Japanese and Korean). Supports nested block-level elements (such as P, DIV),